1. Field of the Invention:
This invention relates to an improvement in an electromagnetic device for driving the shutter of a camera.
2. Description of the Prior Art:
It has been known to use a reciprocating rotary electromagnetic drive source for electromagnetically driving shutter blades or stop blades. The known conventional drive sources used for this purpose include a moving coil type and a moving magnet type. Both types are arranged to drive shutter or stop blades by the rotation of a rotor to an extent not exceeding one half turn. However, it is preferable to use the moving magnet type since it permits simplification of the structural arrangement.
In the conventional electromagnetic drive source of the moving magnet type, an output shaft is directly attached to a magnet while a field coil is divided into two parts to avoid interference with the output shaft. Such an arrangement, however, not only makes it difficult to wind the coil but also does not give a sufficient output because of the lack of a coil in the magnetizing direction, namely on the diameter of the magnet, thus resulting in low magnetic flux density of the coil.